Valve actuators are used to operate valves and are manufactured in numerous shapes, sizes, forms, and have a wide variety of utilities. It is common for an operator of a valve actuator to want to know the specific position of a valve. Absolute encoders and incremental encoders have been utilized with valve actuators to determine the position of a valve. The encoders monitor the position of the valve actuator to determine the corresponding position of a valve.
Absolute encoders utilize a unique signature for each position of a valve actuator. Absolute encoders often use either a single disc or multiple discs that are rotated as a valve actuator moves to different positions. The single or multiple discs of an absolute encoder have markings, different combinations of which provide a unique signature for each position of a valve actuator. This unique signature is analyzed at any time to determine the position of the valve actuator.
Incremental encoders, on the other hand, do not have a unique signature for each position of the valve actuator. Instead, incremental encoders monitor changes in the valve actuator relative to an arbitrary starting point, such as the fully closed position of a valve. An incremental encoder, also referred to as a relative encoder, is often a single disc with a series of duplicate markings around the edge of the disc. As the disc is rotated, each time one of the marks passes a point, a change in position is recorded. As long as the marks are recorded in the memory of a computer, then the valve actuator position is known.
Absolute encoders have the benefit that if power is lost, position information is not lost as well. When power is restored, the unique signature is analyzed to determine position information. If the computer memory of an incremental encoder loses power, then position information is lost. However, absolute encoders are more susceptible to damage, wear, and misalignment than incremental encoders.